Diatomaceous earth fillers for papermaking



Patented Jan. 2, 1945 UNITED DIATOMACEOUS EARTH FILLERS FOR PAPERMAKING Milo A. Harrison, Hermosa Beach, Calif., assignor to The Dicalite Company, Los Angeles, Calif a corporation of Nevada No Drawing. Application September 21, 1942, Serial No. 459,224

2 Claims. (Cl. 106- 288) The instant application is va continuation-inpart of my copending application Serial No, 418,851, filed November 12, 1941, under the title Acidified diatomaceous earth filter-aids, the

said-copending application being in turn a division of my copending application Serial No. 201,188, filed April 9, 1938, under the same title,

which eventuated in Patent 2,296,850, issued September 29, 1943. I

In the making of many types of paper it is known to use finely comminuted diatomaceous earth as a filling or loading agent. In most of the uses described in the prior art -as for example in making newsprint, .boxboard, and felt for' saturation-a slight discoloration of the paper is immaterial. In the making of line white papers, I such as book, magazine, and ledger papers, it is requisite that the paperbe of the maximum ossible whiteness or brightness, and to this end it is customary to add titanium dioxide or other costly white pigments to the furnish, and to bleach the pulp with chlorine.

Finely comminuted diatomaceous earth is a highly advantageous substitute for other loading agents in the making of paper as it considerably facilitates the formation of the sheet, promotes possible that the effect is due primarily to the I have discovered that this darkening effect may be inhibited and all the advantages attendant on the use of this filler may be realized by the addi-- tion to the earth, or to the furnish at the time of adding the earth, of a relatively minute quantity,

of an acid substance compatible with the furnish. This acid substance may be paper-makers alum, or tartaric acid, but I find that citric acid is most suitable as producing a paper of greater brightness than any other acid of which I know. .The mineral acids are undesirable additions to any paper furnish,

I have no adequate explanation either of the loss of brightness which may follow the use of the unacidifled earth or of the corrective effect of an additionof acid. I have observed that the darkening effect is rarely produced unless the furnish contains some ground wood pulp, and it is possible that the darkening is due to reaction between soluble iron compounds in the earth and the tannin content of the wood pulp. It is also increase in pH value of the furnish which is most *likely to occur in the use of flux-calcined (procrapid drainage on the Fourdrinier wire, reduces steam consumption in drying, and gives a highly satisfactory printing or writing surface, Further, as the flux-calcined grades suitable for this purpose are of a high degree of whiteness, this earth may be substituted in part for titanium dioxide,

or may be used to increase the brightness of the paper in lieu of chlorine bleaching when, as at present, this agent is impossible to obtain.

I have observed, however, that in this use of diatomaceous earth the benefit of increased brightness is often not attained, and this par ticularly in the addition to the furnish of earth which has been calcined in the presence of a flux such as common'salt, sodium carbonate, or sodium silicate. Instead, while the change in color is not appreciable in the furnish itself or in the wet sheet formed from it, the dried andfinished paper is often materially darker or less bright than a paper made from a furnish of the same character but with a diflerent loading material.

This darkening of the color of the paper is quite erratic in its occurrence though, as said,'it is most likely to appear in the use of the flux-calcined products and least likely ofoccurrence in the use of the natural (uncalcined) earths which, however, are seldom of sufficient whiteness and purity to make .them useful in P per m The havior in this respect of the calcined earths which have not been fluxed is not known as these prodnets are, almost without exception, gray or pinkish and darken the paper by pigmentation in the expected manner.

- the furnish prior to or during the step of earth essed) earths.

Be this as it may, I have found that if the quantit of acid added to the earth or to the .furnish is suflicient to prevent any material addition. It is not known, nor is it believed, that the acid produces any change in the earth itself acid substance in quantity suiiicient to neutralize 

